Scientists began developing and using chemotherapy drugs to fight cancer in the 1940s, but because the mechanisms by which previously healthy tissue became cancerous were poorly understood, early treatments were relatively nonspecific. Not until the 1970s, in fact, did scientists really begin to understand the true origins of this disease. "Until we knew what was wrong with the cancer cell," says oncologist Bert Vogelstein of Johns Hopkins University, "we couldn't even think about ways of targeting treatment."

Finding the Source

In the 1970s great strides toward understanding cancer on a genetic level were taken, first by Harold Varmus and Mike Bishop in 1970, then by Arnold Levine in 1979. Varmus and Bishop began their research at the University of California at San Francisco with a virus that was known to cause a type of cancer, called a sarcoma, in chickens. Named for the scientist...